Reworked the "new" bridging to respect the bridge_flow_ratio

by maintaining extrusion spacing, but modifying the extrusion width
and / or height.

src/libslic3r/Fill/Fill.cpp

@@ -28,6 +28,8 @@ struct SurfaceFillParams
 //    coordf_t    	overlap = 0.;
     // Angle as provided by the region config, in radians.
     float       	angle = 0.f;
+    // Is bridging used for this fill? Bridging parameters may be used even if this->flow.bridge() is not set.
+    bool 			bridge;
     // Non-negative for a bridge.
     float 			bridge_angle = 0.f;
 
@@ -73,18 +75,19 @@ struct SurfaceFillParams
 		RETURN_COMPARE_NON_EQUAL(flow.width());
 		RETURN_COMPARE_NON_EQUAL(flow.height());
 		RETURN_COMPARE_NON_EQUAL(flow.nozzle_diameter());
-		RETURN_COMPARE_NON_EQUAL_TYPED(unsigned, flow.bridge());
+		RETURN_COMPARE_NON_EQUAL_TYPED(unsigned, bridge);
 		RETURN_COMPARE_NON_EQUAL_TYPED(unsigned, extrusion_role);
 		return false;
 	}
 
 	bool operator==(const SurfaceFillParams &rhs) const {
 		return  this->extruder 			== rhs.extruder 		&&
-				this->pattern 			== rhs.pattern 			&&
 				this->pattern 			== rhs.pattern 			&&
 				this->spacing 			== rhs.spacing 			&&
 //				this->overlap 			== rhs.overlap 			&&
 				this->angle   			== rhs.angle   			&&
+				this->bridge   			== rhs.bridge   		&&
+//				this->bridge_angle 		== rhs.bridge_angle		&&
 				this->density   		== rhs.density   		&&
 //				this->dont_adjust   	== rhs.dont_adjust 		&&
 				this->anchor_length  	== rhs.anchor_length    &&
@@ -128,6 +131,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 
 		        if (surface.is_solid()) {
 		            params.density = 100.f;
+					//FIXME for non-thick bridges, shall we allow a bottom surface pattern?
 		            params.pattern = (surface.is_external() && ! is_bridge) ? 
 						(surface.is_top() ? region_config.top_fill_pattern.value : region_config.bottom_fill_pattern.value) :
 		                region_config.top_fill_pattern == ipMonotonic ? ipMonotonic : ipRectilinear;
@@ -144,9 +148,10 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		        params.angle 		= float(Geometry::deg2rad(region_config.fill_angle.value));
 		        
 		        // Calculate the actual flow we'll be using for this infill.
-				params.flow = is_bridge || Fill::use_bridge_flow(params.pattern) ?
+		        params.bridge = is_bridge || Fill::use_bridge_flow(params.pattern);
+				params.flow   = params.bridge ?
 					layerm.bridging_flow(extrusion_role) :
-					layerm.region()->flow(*layer.object(), extrusion_role, (surface.thickness == -1) ? layer.height : surface.thickness, layer.id() == 0);
+					layerm.flow(extrusion_role, (surface.thickness == -1) ? layer.height : surface.thickness);
 
 				// Calculate flow spacing for infill pattern generation.
 		        if (surface.is_solid() || is_bridge) {
@@ -159,7 +164,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		            // for all layers, for avoiding the ugly effect of
 		            // misaligned infill on first layer because of different extrusion width and
 		            // layer height
-		            params.spacing = layerm.region()->flow(*layer.object(), frInfill, layer.object()->config().layer_height).spacing();
+		            params.spacing = layerm.flow(frInfill, layer.object()->config().layer_height).spacing();
 		            // Anchor a sparse infill to inner perimeters with the following anchor length:
 			        params.anchor_length = float(region_config.infill_anchor);
 					if (region_config.infill_anchor.percent)
@@ -278,7 +283,7 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		        params.extrusion_role = erInternalInfill;
 		        params.angle 		= float(Geometry::deg2rad(layerm.region()->config().fill_angle.value));
 		        // calculate the actual flow we'll be using for this infill
-				params.flow = layerm.region()->flow(*layer.object(), frSolidInfill, layer.height, layer.id() == 0);
+				params.flow = layerm.flow(frSolidInfill);
 		        params.spacing = params.flow.spacing();	        
 				surface_fills.emplace_back(params);
 				surface_fills.back().surface.surface_type = stInternalSolid;
@@ -346,9 +351,9 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
         f->adapt_fill_octree = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
 
         // calculate flow spacing for infill pattern generation
-        bool using_internal_flow = ! surface_fill.surface.is_solid() && ! surface_fill.params.flow.bridge();
+        bool using_internal_flow = ! surface_fill.surface.is_solid() && ! surface_fill.params.bridge;
         double link_max_length = 0.;
-        if (! surface_fill.params.flow.bridge()) {
+        if (! surface_fill.params.bridge) {
 #if 0
             link_max_length = layerm.region()->config().get_abs_value(surface.is_external() ? "external_fill_link_max_length" : "fill_link_max_length", flow.spacing());
 //            printf("flow spacing: %f,  is_external: %d, link_max_length: %lf\n", flow.spacing(), int(surface.is_external()), link_max_length);
@@ -389,9 +394,7 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 		            // so we can safely ignore the slight variation that might have
 		            // been applied to f->spacing
 		        } else {
-		            Flow new_flow = surface_fill.params.flow.bridge() ?
+		            Flow new_flow   = surface_fill.params.flow.with_spacing(float(f->spacing));
-		            	Flow::bridging_flow_from_spacing(float(f->spacing), surface_fill.params.flow.nozzle_diameter()) :
-		            	Flow::new_from_spacing(float(f->spacing), surface_fill.params.flow.nozzle_diameter(), surface_fill.params.flow.height());
 		        	flow_mm3_per_mm = new_flow.mm3_per_mm();
 		        	flow_width      = new_flow.width();
 		        }
@@ -601,9 +604,9 @@ void Layer::make_ironing()
         fill.spacing = ironing_params.line_spacing;
         fill.angle = float(ironing_params.angle + 0.25 * M_PI);
         fill.link_max_length = (coord_t)scale_(3. * fill.spacing);
-		double height = ironing_params.height * fill.spacing / nozzle_dmr;
+		double extrusion_height = ironing_params.height * fill.spacing / nozzle_dmr;
-        Flow flow = Flow::new_from_spacing(float(nozzle_dmr), 0., float(height));
+		float  extrusion_width  = Flow::rounded_rectangle_extrusion_width_from_spacing(float(nozzle_dmr), float(extrusion_height));
-        double flow_mm3_per_mm = flow.mm3_per_mm();
+		double flow_mm3_per_mm = nozzle_dmr * extrusion_height;
         Surface surface_fill(stTop, ExPolygon());
         for (ExPolygon &expoly : ironing_areas) {
 			surface_fill.expolygon = std::move(expoly);
@@ -621,7 +624,7 @@ void Layer::make_ironing()
 		        extrusion_entities_append_paths(
 		            eec->entities, std::move(polylines),
 		            erIroning,
-		            flow_mm3_per_mm, float(flow.width()), float(height));
+		            flow_mm3_per_mm, extrusion_width, float(extrusion_height));
 		    }
 		}
 	}

src/libslic3r/Flow.cpp

@@ -6,12 +6,6 @@
 
 #include <boost/algorithm/string/predicate.hpp>
 
-// Overlap factor of perimeter lines. Currently no overlap.
-// #define HAS_PERIMETER_LINE_OVERLAP
-#ifdef HAS_PERIMETER_LINE_OVERLAP
-    #define PERIMETER_LINE_OVERLAP_FACTOR 1.0
-#endif
-
 // Mark string for localization and translate.
 #define L(s) Slic3r::I18N::translate(s)
 
@@ -142,62 +136,82 @@ Flow Flow::new_from_config_width(FlowRole role, const ConfigOptionFloatOrPercent
         w = float(width.get_abs_value(height));
     }
     
-    return Flow(w, height, nozzle_diameter, false);
+    return Flow(w, height, rounded_rectangle_extrusion_spacing(w, height), nozzle_diameter, false);
 }
 
-// This constructor builds a Flow object from a given centerline spacing.
+// Adjust extrusion flow for new extrusion line spacing, maintaining the old spacing between extrusions.
-Flow Flow::new_from_spacing(float spacing, float nozzle_diameter, float height) 
+Flow Flow::with_spacing(float new_spacing) const
 {
-    if (height <= 0) 
+    Flow out = *this;
-        throw Slic3r::InvalidArgument("Invalid flow height supplied to new_from_spacing()");
+    if (m_bridge) {
-    // Calculate width from spacing.
+        // Diameter of the rounded extrusion.
-    // For normal extrusons, extrusion width is wider than the spacing due to the rounding and squishing of the extrusions.
+        assert(m_width == m_height);
-    float width = float(
+        float gap          = m_spacing - m_width;
-#ifdef HAS_PERIMETER_LINE_OVERLAP
+        auto  new_diameter = new_spacing - gap;
-        (spacing + PERIMETER_LINE_OVERLAP_FACTOR * height * (1. - 0.25 * PI));
+        out.m_width        = out.m_height = new_diameter;
-#else
+    } else {
-        (spacing + height * (1. - 0.25 * PI)));
+        out.m_width += new_spacing - m_spacing;
-#endif
+        if (out.m_width < out.m_height)
-    return Flow(width, height, nozzle_diameter);
+            throw Slic3r::InvalidArgument("Invalid spacing supplied to Flow::with_spacing()");
+    }
+    out.m_spacing = new_spacing;
+    return out;
 }
 
-// This method returns the centerline spacing between two adjacent extrusions 
+// Adjust the width / height of a rounded extrusion model to reach the prescribed cross section area while maintaining extrusion spacing.
-// having the same extrusion width (and other properties).
+Flow Flow::with_cross_section(float area_new) const
-float Flow::spacing() const 
 {
-#ifdef HAS_PERIMETER_LINE_OVERLAP
+    assert(! m_bridge);
-    if (m_bridge)
+    assert(flow.width() >= flow.height());
-        return m_width + BRIDGE_EXTRA_SPACING;
+
-    // rectangle with semicircles at the ends
+    // Adjust for bridge_flow_ratio, maintain the extrusion spacing.
-    float min_flow_spacing = m_width - m_height * (1. - 0.25 * PI);
+    float area = this->mm3_per_mm();
-    float res = m_width - PERIMETER_LINE_OVERLAP_FACTOR * (m_width - min_flow_spacing);
+    if (area_new > area + EPSILON) {
-#else
+        // Increasing the flow rate.
-    float res = float(m_bridge ? (m_width + BRIDGE_EXTRA_SPACING) : (m_width - m_height * (1. - 0.25 * PI)));
+        float new_full_spacing = area_new / m_height;
-#endif
+        if (new_full_spacing > m_spacing) {
-//    assert(res > 0.f);
+            // Filling up the spacing without an air gap. Grow the extrusion in height.
-	if (res <= 0.f)
+            float height = area_new / m_spacing;
-		throw FlowErrorNegativeSpacing();
+            return Flow(rounded_rectangle_extrusion_width_from_spacing(m_spacing, height), height, m_spacing, m_nozzle_diameter, false);
-	return res;
+        } else {
+            return this->with_width(rounded_rectangle_extrusion_width_from_spacing(area / m_height, m_height));
+        }
+    } else if (area_new < area - EPSILON) {
+        // Decreasing the flow rate.
+        float width_new = m_width - (area - area_new) / m_height;
+        assert(width_dif > 0);
+        if (width_new > m_height) {
+            // Shrink the extrusion width.
+            return this->with_width(width_new);
+        } else {
+            // Create a rounded extrusion.
+            auto dmr = float(sqrt(area_new / M_PI));
+            return Flow(dmr, dmr, m_spacing, m_nozzle_diameter, false);
+        }
+    } else
+        return *this;
 }
 
-// This method returns the centerline spacing between an extrusion using this
+float Flow::rounded_rectangle_extrusion_spacing(float width, float height)
-// flow and another one using another flow.
-// this->spacing(other) shall return the same value as other.spacing(*this)
-float Flow::spacing(const Flow &other) const
 {
-    assert(m_height == other.m_height);
+    auto out = width - height * float(1. - 0.25 * PI);
-    assert(m_bridge == other.m_bridge);
+    if (out <= 0.f)
-    float res = float(m_bridge ? 
+        throw FlowErrorNegativeSpacing();
-        0.5 * m_width + 0.5 * other.m_width + BRIDGE_EXTRA_SPACING :
+    return out;
-        0.5 * this->spacing() + 0.5 * other.spacing());
+}
-//    assert(res > 0.f);
+
-	if (res <= 0.f)
+float Flow::rounded_rectangle_extrusion_width_from_spacing(float spacing, float height)
-		throw FlowErrorNegativeSpacing();
+{
-	return res;
+    return float(spacing + height * (1. - 0.25 * PI));
+}
+
+float Flow::bridge_extrusion_spacing(float dmr)
+{
+    return dmr + BRIDGE_EXTRA_SPACING;
 }
 
 // This method returns extrusion volume per head move unit.
-double Flow::mm3_per_mm() const 
+double Flow::mm3_per_mm() const
 {
     float res = m_bridge ?
         // Area of a circle with dmr of this->width.

src/libslic3r/Flow.hpp

@@ -51,26 +51,26 @@ public:
 class Flow
 {
 public:
+    Flow() = default;
+    Flow(float width, float height, float nozzle_diameter) :
+        Flow(width, height, rounded_rectangle_extrusion_spacing(width, height), nozzle_diameter, false) {}
+
     // Non bridging flow: Maximum width of an extrusion with semicircles at the ends.
     // Bridging flow: Bridge thread diameter.
-    float width()           const { return m_width; }
+    float   width()           const { return m_width; }
+    coord_t scaled_width()    const { return coord_t(scale_(m_width)); }
     // Non bridging flow: Layer height.
     // Bridging flow: Bridge thread diameter = layer height.
-    float height()          const { return m_height; }
+    float   height()          const { return m_height; }
+    // Spacing between the extrusion centerlines.
+    float   spacing()         const { return m_spacing; }
+    coord_t scaled_spacing()  const { return coord_t(scale_(m_spacing)); }
     // Nozzle diameter. 
-    float nozzle_diameter() const { return m_nozzle_diameter; }
+    float   nozzle_diameter() const { return m_nozzle_diameter; }
     // Is it a bridge?
-    bool  bridge()          const { return m_bridge; }
+    bool    bridge()          const { return m_bridge; }
-    
+    // Cross section area of the extrusion.
-    Flow() = default;
+    double  mm3_per_mm()      const;
-    Flow(float w, float h, float nozzle_diameter) : Flow(w, h, nozzle_diameter, false) {}
-
-    float   spacing() const;
-    float   spacing(const Flow &other) const;
-    double  mm3_per_mm() const;
-    coord_t scaled_width() const { return coord_t(scale_(m_width)); }
-    coord_t scaled_spacing() const { return coord_t(scale_(this->spacing())); }
-    coord_t scaled_spacing(const Flow &other) const { return coord_t(scale_(this->spacing(other))); }
 
     // Elephant foot compensation spacing to be used to detect narrow parts, where the elephant foot compensation cannot be applied.
     // To be used on frExternalPerimeter only.
@@ -80,18 +80,30 @@ public:
 
     bool operator==(const Flow &rhs) const { return m_width == rhs.m_width && m_height == rhs.m_height && m_nozzle_diameter == rhs.m_nozzle_diameter && m_bridge == rhs.m_bridge; }
 
-    Flow        with_width (float width)  const { assert(! m_bridge); return Flow(width, m_height, m_nozzle_diameter, m_bridge); }
+    Flow        with_width (float width)  const { 
-    Flow        with_height(float height) const { assert(! m_bridge); return Flow(m_width, height, m_nozzle_diameter, m_bridge); }
+        assert(! m_bridge); 
+        return Flow(width, m_height, rounded_rectangle_extrusion_spacing(width, m_height), m_nozzle_diameter, m_bridge);
+    }
+    Flow        with_height(float height) const { 
+        assert(! m_bridge); 
+        return Flow(m_width, height, rounded_rectangle_extrusion_spacing(m_width, height), m_nozzle_diameter, m_bridge);
+    }
+    // Adjust extrusion flow for new extrusion line spacing, maintaining the old spacing between extrusions.
+    Flow        with_spacing(float spacing) const;
+    // Adjust the width / height of a rounded extrusion model to reach the prescribed cross section area while maintaining extrusion spacing.
+    Flow        with_cross_section(float area) const;
+    Flow        with_flow_ratio(double ratio) const { return this->with_cross_section(this->mm3_per_mm() * ratio); }
+
+    static Flow bridging_flow(float dmr, float nozzle_diameter) { return Flow { dmr, dmr, bridge_extrusion_spacing(dmr), nozzle_diameter, true }; }
 
-    static Flow bridging_flow(float dmr, float nozzle_diameter) { return Flow { dmr, dmr, nozzle_diameter, true }; }
-    static Flow bridging_flow_from_spacing(float spacing, float nozzle_diameter) 
-        { auto dmr = spacing - float(BRIDGE_EXTRA_SPACING); return Flow { dmr, dmr, nozzle_diameter, true }; }
-    
     static Flow new_from_config_width(FlowRole role, const ConfigOptionFloatOrPercent &width, float nozzle_diameter, float height);
-    // Create a flow from the spacing of extrusion lines.
+
-    // This method is used exclusively to calculate new flow of 100% infill, where the extrusion width was allowed to scale
+    // Spacing of extrusions with rounded extrusion model.
-    // to fit a region with integer number of lines.
+    static float rounded_rectangle_extrusion_spacing(float width, float height);
-    static Flow new_from_spacing(float spacing, float nozzle_diameter, float height);
+    // Width of extrusions with rounded extrusion model.
+    static float rounded_rectangle_extrusion_width_from_spacing(float spacing, float height);
+    // Spacing of round thread extrusions.
+    static float bridge_extrusion_spacing(float dmr);
 
     // Sane extrusion width defautl based on nozzle diameter.
     // The defaults were derived from manual Prusa MK3 profiles.
@@ -104,10 +116,12 @@ public:
 	static double extrusion_width(const std::string &opt_key, const ConfigOptionResolver &config, const unsigned int first_printing_extruder = 0);
 
 private:
-    Flow(float w, float h, float nozzle_diameter, bool bridge) : m_width(w), m_height(h), m_nozzle_diameter(nozzle_diameter), m_bridge(bridge) {}
+    Flow(float width, float height, float spacing, float nozzle_diameter, bool bridge) : 
+        m_width(width), m_height(height), m_spacing(spacing), m_nozzle_diameter(nozzle_diameter), m_bridge(bridge) {}
 
     float       m_width { 0 };
     float       m_height { 0 };
+    float       m_spacing { 0 };
     float       m_nozzle_diameter { 0 };
     bool        m_bridge { false };
 };

src/libslic3r/Layer.hpp

@@ -60,6 +60,7 @@ public:
     ExtrusionEntityCollection   fills;
     
     Flow    flow(FlowRole role) const;
+    Flow    flow(FlowRole role, double layer_height) const;
     Flow    bridging_flow(FlowRole role) const;
 
     void    slices_to_fill_surfaces_clipped();

src/libslic3r/LayerRegion.cpp

@@ -17,12 +17,29 @@ namespace Slic3r {
 
 Flow LayerRegion::flow(FlowRole role) const
 {
-    return m_region->flow(*m_layer->object(), role, m_layer->height, m_layer->id() == 0);
+    return this->flow(role, m_layer->height);
+}
+
+Flow LayerRegion::flow(FlowRole role, double layer_height) const
+{
+    return m_region->flow(*m_layer->object(), role, layer_height, m_layer->id() == 0);
 }
 
 Flow LayerRegion::bridging_flow(FlowRole role) const
-{ 
+{
-    return this->layer()->object()->config().thick_bridges ? m_region->bridging_flow(role) : this->flow(role);
+    const PrintRegion       &region         = *this->region();
+    const PrintRegionConfig &region_config  = region.config();
+    if (this->layer()->object()->config().thick_bridges) {
+        // The old Slic3r way (different from all other slicers): Use rounded extrusions.
+        // Get the configured nozzle_diameter for the extruder associated to the flow role requested.
+        // Here this->extruder(role) - 1 may underflow to MAX_INT, but then the get_at() will follback to zero'th element, so everything is all right.
+        auto nozzle_diameter = float(region.print()->config().nozzle_diameter.get_at(region.extruder(role) - 1));
+        // Applies default bridge spacing.
+        return Flow::bridging_flow(float(sqrt(region_config.bridge_flow_ratio)) * nozzle_diameter, nozzle_diameter);
+    } else {
+        // The same way as other slicers: Use normal extrusions. Apply bridge_flow_ratio while maintaining the original spacing.
+        return this->flow(role).with_flow_ratio(region_config.bridge_flow_ratio);
+    }
 }
 
 // Fill in layerm->fill_surfaces by trimming the layerm->slices by the cummulative layerm->fill_surfaces.

src/libslic3r/PerimeterGenerator.cpp

@@ -286,7 +286,7 @@ void PerimeterGenerator::process()
     m_ext_mm3_per_mm           		= this->ext_perimeter_flow.mm3_per_mm();
     coord_t ext_perimeter_width     = this->ext_perimeter_flow.scaled_width();
     coord_t ext_perimeter_spacing   = this->ext_perimeter_flow.scaled_spacing();
-    coord_t ext_perimeter_spacing2  = this->ext_perimeter_flow.scaled_spacing(this->perimeter_flow);
+    coord_t ext_perimeter_spacing2  = scaled<coord_t>(0.5f * (this->ext_perimeter_flow.spacing() + this->perimeter_flow.spacing()));
     
     // overhang perimeters
     m_mm3_per_mm_overhang      		= this->overhang_flow.mm3_per_mm();

src/libslic3r/Print.hpp

@@ -66,7 +66,6 @@ public:
 	// 1-based extruder identifier for this region and role.
 	unsigned int 				extruder(FlowRole role) const;
     Flow                        flow(const PrintObject &object, FlowRole role, double layer_height, bool first_layer = false) const;
-    Flow                        bridging_flow(FlowRole role) const;
     // Average diameter of nozzles participating on extruding this region.
     coordf_t                    nozzle_dmr_avg(const PrintConfig &print_config) const;
     // Average diameter of nozzles participating on extruding this region.

src/libslic3r/PrintObject.cpp

@@ -1457,19 +1457,18 @@ void PrintObject::bridge_over_infill()
         const PrintRegion &region = *m_print->regions()[region_id];
         
         // skip bridging in case there are no voids
-        if (region.config().fill_density.value == 100) continue;
+        if (region.config().fill_density.value == 100)
-        
+            continue;
-        // get bridge flow
+
-        Flow bridge_flow = region.bridging_flow(frSolidInfill);
-        
 		for (LayerPtrs::iterator layer_it = m_layers.begin(); layer_it != m_layers.end(); ++ layer_it) {
             // skip first layer
 			if (layer_it == m_layers.begin())
                 continue;
             
-            Layer* layer        = *layer_it;
+            Layer       *layer       = *layer_it;
-            LayerRegion* layerm = layer->m_regions[region_id];
+            LayerRegion *layerm      = layer->m_regions[region_id];
-            
+            Flow         bridge_flow = layerm->bridging_flow(frSolidInfill);
+
             // extract the stInternalSolid surfaces that might be transformed into bridges
             Polygons internal_solid;
             layerm->fill_surfaces.filter_by_type(stInternalSolid, &internal_solid);

src/libslic3r/PrintRegion.cpp

@@ -48,17 +48,6 @@ Flow PrintRegion::flow(const PrintObject &object, FlowRole role, double layer_he
     return Flow::new_from_config_width(role, config_width, nozzle_diameter, float(layer_height));
 }
 
-Flow PrintRegion::bridging_flow(FlowRole role) const
-{
-    // Get the configured nozzle_diameter for the extruder associated to the flow role requested.
-    // Here this->extruder(role) - 1 may underflow to MAX_INT, but then the get_at() will follback to zero'th element, so everything is all right.
-    auto nozzle_diameter = float(m_print->config().nozzle_diameter.get_at(this->extruder(role) - 1));
-    double bfr = m_config.bridge_flow_ratio;
-    if (bfr != 1.)
-        bfr = sqrt(bfr);
-    return Flow::bridging_flow(float(bfr) * nozzle_diameter, nozzle_diameter);
-}
-
 coordf_t PrintRegion::nozzle_dmr_avg(const PrintConfig &print_config) const
 {
     return (print_config.nozzle_diameter.get_at(m_config.perimeter_extruder.value    - 1) + 

src/libslic3r/SupportMaterial.cpp

@@ -334,7 +334,7 @@ PrintObjectSupportMaterial::PrintObjectSupportMaterial(const PrintObject *object
     for (auto lh : m_print_config->min_layer_height.values)
         m_support_layer_height_min = std::min(m_support_layer_height_min, std::max(0.01, lh));
 
-    if (m_object_config->support_material_interface_layers.value == 0) {
+    if (m_slicing_params.soluble_interface) {
         // No interface layers allowed, print everything with the base support pattern.
         m_support_material_interface_flow = m_support_material_flow;
     }
@@ -342,11 +342,21 @@ PrintObjectSupportMaterial::PrintObjectSupportMaterial(const PrintObject *object
     // Evaluate the XY gap between the object outer perimeters and the support structures.
     // Evaluate the XY gap between the object outer perimeters and the support structures.
     coordf_t external_perimeter_width = 0.;
+    size_t   num_nonempty_regions = 0;
+    coordf_t bridge_flow_ratio = 0;
     for (size_t region_id = 0; region_id < object->region_volumes.size(); ++ region_id)
-        if (! object->region_volumes[region_id].empty())
+        if (! object->region_volumes[region_id].empty()) {
-            external_perimeter_width = std::max(external_perimeter_width,
+            ++ num_nonempty_regions;
-                (coordf_t)object->print()->get_region(region_id)->flow(*object, frExternalPerimeter, slicing_params.layer_height).width());
+            const PrintRegion &region = *object->print()->get_region(region_id);
+            external_perimeter_width = std::max(external_perimeter_width, coordf_t(region.flow(*object, frExternalPerimeter, slicing_params.layer_height).width()));
+            bridge_flow_ratio += region.config().bridge_flow_ratio;
+        }
     m_gap_xy = m_object_config->support_material_xy_spacing.get_abs_value(external_perimeter_width);
+    bridge_flow_ratio /= num_nonempty_regions;
+
+    m_support_material_bottom_interface_flow = m_slicing_params.soluble_interface || ! m_object_config->thick_bridges ?
+        m_support_material_interface_flow.with_flow_ratio(bridge_flow_ratio) :
+        Flow::bridging_flow(bridge_flow_ratio * m_support_material_interface_flow.nozzle_diameter(), m_support_material_interface_flow.nozzle_diameter());
 
     m_can_merge_support_regions = m_object_config->support_material_extruder.value == m_object_config->support_material_interface_extruder.value;
     if (! m_can_merge_support_regions && (m_object_config->support_material_extruder.value == 0 || m_object_config->support_material_interface_extruder.value == 0)) {
@@ -1231,8 +1241,8 @@ namespace SupportMaterialInternal {
             // since we're dealing with bridges, we can't assume width is larger than spacing,
             // so we take the largest value and also apply safety offset to be ensure no gaps
             // are left in between
-            Flow bridge_flow = layerm->bridging_flow(frPerimeter);
+            Flow perimeter_bridge_flow = layerm->bridging_flow(frPerimeter);
-            float w = float(std::max(bridge_flow.scaled_width(), bridge_flow.scaled_spacing()));
+            float w = float(std::max(perimeter_bridge_flow.scaled_width(), perimeter_bridge_flow.scaled_spacing()));
             for (Polyline &polyline : overhang_perimeters)
                 if (polyline.is_straight()) {
                     // This is a bridge 
@@ -1879,13 +1889,8 @@ PrintObjectSupportMaterial::MyLayersPtr PrintObjectSupportMaterial::bottom_conta
                             layer_new.height  = m_slicing_params.soluble_interface ? 
                                 // Align the interface layer with the object's layer height.
                                 object.layers()[layer_id + 1]->height :
-                                // Place a bridge flow interface layer over the top surface.
+                                // Place a bridge flow interface layer or the normal flow interface layer over the top surface.
-                                //FIXME Check whether the bottom bridging surfaces are extruded correctly (no bridging flow correction applied?)
+                                m_support_material_bottom_interface_flow.height();
-                                // According to Jindrich the bottom surfaces work well.
-                                //FIXME test the bridging flow instead?
-                                m_object_config->thick_bridges.value ? m_support_material_interface_flow.nozzle_diameter() :
-                                // Take the default layer height.
-                                m_object_config->layer_height;
                             layer_new.print_z = m_slicing_params.soluble_interface ? object.layers()[layer_id + 1]->print_z :
                                 layer.print_z + layer_new.height + m_object_config->support_material_contact_distance.value;
                             layer_new.bottom_z = layer.print_z;
@@ -3497,7 +3502,7 @@ void PrintObjectSupportMaterial::generate_toolpaths(
     coordf_t interface_density  = std::min(1., m_support_material_interface_flow.spacing() / interface_spacing);
     coordf_t support_spacing    = m_object_config->support_material_spacing.value + m_support_material_flow.spacing();
     coordf_t support_density    = std::min(1., m_support_material_flow.spacing() / support_spacing);
-    if (m_object_config->support_material_interface_layers.value == 0) {
+    if (m_slicing_params.soluble_interface) {
         // No interface layers allowed, print everything with the base support pattern.
         interface_spacing = support_spacing;
         interface_density = support_density;
@@ -3738,13 +3743,12 @@ void PrintObjectSupportMaterial::generate_toolpaths(
                 MyLayerExtruded &layer_ex = (i == 0) ? top_contact_layer : (i == 1 ? bottom_contact_layer : interface_layer);
                 if (layer_ex.empty() || layer_ex.polygons_to_extrude().empty())
                     continue;
-                bool interface_as_base = (&layer_ex == &interface_layer) && m_object_config->support_material_interface_layers.value == 0;
+                bool interface_as_base = (&layer_ex == &interface_layer) && m_slicing_params.soluble_interface;
                 //FIXME Bottom interfaces are extruded with the briding flow. Some bridging layers have its height slightly reduced, therefore
                 // the bridging flow does not quite apply. Reduce the flow to area of an ellipse? (A = pi * a * b)
                 auto interface_flow = layer_ex.layer->bridging ?
-                    Flow::bridging_flow(layer_ex.layer->height, m_support_material_interface_flow.nozzle_diameter()) :
+                    Flow::bridging_flow(layer_ex.layer->height, m_support_material_bottom_interface_flow.nozzle_diameter()) :
-                    Flow(interface_as_base ? m_support_material_flow.width() : m_support_material_interface_flow.width(), 
+                    (interface_as_base ? &m_support_material_flow : &m_support_material_interface_flow)->with_height(float(layer_ex.layer->height));
-                        float(layer_ex.layer->height), m_support_material_interface_flow.nozzle_diameter());
                 filler_interface->angle = interface_as_base ?
                         // If zero interface layers are configured, use the same angle as for the base layers.
                         angles[support_layer_id % angles.size()] :

src/libslic3r/SupportMaterial.hpp

@@ -244,6 +244,7 @@ private:
 	Flow 			 	 m_first_layer_flow;
 	Flow 			 	 m_support_material_flow;
 	Flow 			 	 m_support_material_interface_flow;
+	Flow 				 m_support_material_bottom_interface_flow;
 	// Is merging of regions allowed? Could the interface & base support regions be printed with the same extruder?
 	bool 				 m_can_merge_support_regions;
 

xs/xsp/Flow.xsp

@@ -16,8 +16,6 @@
     float nozzle_diameter();
     bool bridge();
     float spacing();
-    float spacing_to(Flow* other)
-        %code{% RETVAL = THIS->spacing(*other); %};
     int   scaled_width();
     int   scaled_spacing();
     double mm3_per_mm();